The present invention is directed to bicycles and, more particularly, to a bicycle shift control device that responds to a manually operated switch.
Bicycle transmissions typically include internal transmissions and external transmissions. Internal transmissions usually comprise an internal hub transmission that employs one or more planetary gear mechanisms that set a plurality of gear ratios corresponding to speed stages. A manually operated shift control device for internal hub transmissions may comprise first and second manually operated levers, wherein the first lever is used to set progressively higher gear ratios, and the second lever is used to set progressively lower gear ratios.
External transmissions usually comprise front and/or rear derailleurs that engage a chain with one or more sprockets that rotate with the pedal crank or the rear wheel. A common external transmission comprises a front derailleur that engages a chain with one of a plurality of front sprockets that rotate with the pedal crank, and a rear derailleur that engages the chain with one of a plurality of rear sprockets that rotate with the rear wheel. Manually operated shift control devices for such transmissions may comprise a separate manually operated shift control device for each derailleur, wherein each shift control device includes first and second manually operated levers. Such a shift control device arrangement is disclosed in Japanese Laid Open Patent Application No. 5-319355. In this arrangement, the rear shift control device is mounted at the right side of the bicycle handlebar, and the front shift control device is mounted at the left side of the handlebar. For the rear shift control device, the first lever is operated with the index finger to upshift the rear derailleur, and the second lever is operated with the thumb to downshift the derailleur. By contrast, for the front shift control device, the first lever is operated with the index finger to downshift the front derailleur, and the second lever is operated with the thumb to upshift the front derailleur.
Since all four levers must be skillfully used taking into account the opposite operating nature of the front and rear shift control devices, a novice rider may have trouble understanding which shift lever should be used to set a desired speed stage. To overcome this problem, some bicycles are equipped with automatic shift control devices that automatically cause a control device to set the front and rear derailleurs to the proper front and rear sprockets, respectively, according to bicycle speed. However, since such automatic operation is performed without regard to the intentions of the rider, the speed stage of the transmission may be changed against the intentions of the rider. Such unintended changes also result in unexpectedly increased or decreased pedaling resistance, thus causing further discomfort to the rider.